The invention is in the microelectronics field and is particularly concerned with devices making use of focused emissions from electron emitters.
An emitter emits electrons in response to an electrical signal. Controlling these emissions forms a basis to create useful electrical and optical effects. For example, emissions can affect various media to produce memory and display effects, or be used for electron-beam lithography to produce submicron features in wafers to form microelectronic circuits. Production of focused beams involves the fabrication of an emitter and focusing structure, typically an electrostatic lens.
Emitter surfaces are sensitive to surface conditions and to processing of the emitter surface or processing on the emitter surface. This sensitivity extends across the spectrum of different types of electron emitters, including thermionic emitters, flat emitters such as polysilicon emitters, MOS (metal-oxide-semiconductor) emitters, MIS (metal-insulator-semiconductor) emitters, and MIM (metal-insulator-metal) emitters. This list also includes emitters based on different types of carbon films (nanodispersed carbon, diamond-like films, carbon nanotubes) as well as silicon tips and Spindt tip emitters. Fabrication of lenses and other structures on the emitter substrate can damage the surface or leave a surface that is not clean. Damage or excess material can harm emitter performance attributes, such as uniformity of emission over a given area or the amount of emission from a given emitter. Delivered current and emission uniformity are important parameters for all kinds of vacuum electron sources, and are critical parameters in high frequency and/or precision e-beam devices. Emission uniformity is especially important for applications such as memory storage and lithography, and the amount of emission obtained is very important for memory storage devices.
Various emitter driven devices, such as memories and displays, make use of a target anode medium. The target anode medium is the focus point for the controlled emissions of electrons. A target anode medium is held at hundreds of volts differential from the emitter/cathode structure. A strong xe2x80x9cpull-downxe2x80x9d attraction therefore exists between the target anode and emitter cathode. This phenomenon manifests strongly in devices having small medium-to-emitter distances, especially where large areas and high applied differential voltages are concerned.
Alignment and focusing length are also important issues in emitter driven devices. Fabrication of lenses on emitter substrates requires the precise alignment of the emitters and the focusing elements. Many high precision alignments are required to properly align a focusing lens with the emitter. With the addition of each focusing element on an emitter substrate, there is also processing complexity, e.g., deep etches that must be stopped at the emitter without damaging or changing the surface of the emitter. The focusing length is also limited to the short distance afforded by the separation of various metal layers in an emitter/focusing lens substrate.
An emitter device of the invention includes a focusing array with plural focusing columns to focus electron emissions from one or more emitters onto a target medium. Relative movement between the target medium and the focused emissions allows each focusing column to focus emissions over an area of the target medium encompassing the movement range.
In a preferred embodiment, separate emitter, focusing array and target medium substrates are used for the manufacture of the preferred device.